Phase-locked loop (PLL) is an auto-controlling circuit system, which is able to track the frequency and the phase of an input signal. The phase-locked loop tracks and locks the phases and the frequencies of an output signal and the input signal, so as to keep the phase and the frequency of the output signal at a predetermined value or in a predetermined range. Currently, the phase-locked loop has been widely used in computers and consumer products.
However, the phase-locked loop is prone to be interfered by noise, and this may cause the time offset problem of the output signal (i.e., the so-called jittering problem) and result in the clock error.